The present invention relates generally to nuclear reactors and more particularly to an improved fuel handling apparatus for a nuclear reactor.
Certain types of nuclear reactors, such as high temperature, gas-cooled reactors (HTGR), typically employ an array of fuel elements which form a core within the interior of the reactor. The core is enclosed within a reactor vessel. It is desirable to remove fuel elements from the reactor core periodically and replace them with new fuel elements. It may also be desirable to shift fuel elements to different positions within the reactor core.
Elongated fuel elements of hexagonal cross-section are commonly stacked upright to form the core. This general type of core construction is described in U.S. Pat. No. 3,383,286 to Paget, which is incorporated herein by reference.
It is known for a device for manipulating fuel elements within a reactor vessel to access the reactor core through an opening in the top of the vessel. In some relatively recently developed reactors, it has been found desirable to utilize the space above the reactor core for heat exchange apparatus and the like, without leaving space for access to the core from above by fuel handling apparatus. With this type of arrangement, it is desirable to access the core through an opening in the side of the reactor vessel.
The various fuel elements are distributed in predetermined locations and typically abut one another at their sides. Accurate placement is necessary in order to position the elements in their locations. Accordingly, it is desirable that fuel handling apparatus be capable of operating with a high degree of precision. In addition, it is desirable that the apparatus lift and lower the elements along vertical paths to avoid excessive friction with adjacent elements.
Friction with adjacent elements may require downward forces in excess of the gravitational force exerted on the element to bring the element to a desired elevational location. Accordingly, the fuel element handling apparatus should be capable of exerting downward force onto the elements as well as upward force.
The vessel herein may be required to support a relatively high pressure differential between its interior and its exterior. To lessen interference with the structure of the vessel, it is desirable that a single penetration of relatively small diameter be sufficient to provide access to the entire core for the fuel handling apparatus. Accordingly, the fuel handling apparatus should fit through a relatively small penetration and include means for accessing fuel elements at various locations within the vessel, and should be capable of carrying a fuel element through a relatively small penetration. In addition, it is desirable that the fuel handling apparatus be capable of transporting fuel elements over relatively long distances both laterally and vertically so that both removal of spent fuel elements from the vessel to a desired remote location and, transportation of new fuel elements from a desired remote location to the interior of the vessel may be accomplished.
It is further desirable that the fuel handling apparatus be adequately sealed to the vessel so that escape of radioactive material from the vessel is avoided or minimized during operation of the apparatus.
The radioactive environment within the vessel excludes certain types of mechanisms from use within the vessel. Hydraulic systems, for example, may not be suitable due to breakdown of hydraulic fluids in the radioactive environment.
There is a need for a fuel handling apparatus which is acceptable for use in a reactor having its refueling port located on the side of the vessel rather than in the top.